Dear Emily,
In the version of SPM you are using I believe the first parameter is the
a hemodynamic time constant that's common to all areas (thats the sigma
parameter in equation 9 of the original 2003 paper on DCM for fMRI).
The other parameters are from the Ballon model which describes the
hemodynamics (eg. blood transit time, rate of signal decay etc. see
Table 1 in 2003 paper).
Specific details can be found in the function spm_dcm_fmri_priors.m
Best,
Will.
Emily L. Parks wrote:
> Dear Will,
>
> Thank you so much your quick response. I very much appreciate it.
> However, I do have further questions:
>
> I see how some of the DCM.Ep matrix matches the intrinsic connection
> matrix (A), the input-dependent connection matrix (B), and the input
> connection matrix (C).
>
> For example, here is a sample DCM.Ep:
>
> *
> *
> *DCM.Ep*
>
>
>
>
> -0.17165
>
>
>
>
> -1
>
> *DCM.A*
> 0
>
>
> -1 0.116
> 0.116122
>
>
> 0 -1
> -1
>
>
>
>
> 0
>
> *DCM.B*
> 0
>
>
> 0 -0.01008
> -0.01008
>
>
> 0 0
> 0
>
>
>
>
> -0.06318
>
> *DCM.C*
> -0.11465
>
>
> -0.06318
> 0.598159
>
>
> -0.11465
> 0.674434
>
>
>
>
> 0.398959
>
>
>
>
> 0.381541
>
>
>
>
> 1.030029
>
>
>
>
> 1.131214
>
>
>
>
> 0.318057
>
>
>
>
> 0.320224
>
>
>
>
> 0.342802
>
>
>
>
> 0.344475
>
>
>
>
> 0.003723
>
>
>
>
> -0.01634
>
>
>
>
>
>
>
> I see how the 2nd - 11th numbers in the DCM.Ep file match DCM.A, DCM.B,
> and DCM.C. However, I don't understand what the first number reflects
> (.17165) or the 12th-23rd numbers (.598159, .674434..... -.01634).
>
> I have checked the other DCM output files (i.e. DCM.pA, DCM.vA, etc),
> but I see no correspondence. Any ideas?
>
> Thank you so much again and have a wonderful day.
>
> Cheers,
> Emily Parks
>
>
>
>
>
>
>
> -------- Original Message --------
> Subject: Re: [SPM] DCM.Ep output
> Date: Mon, 20 Sep 2010 10:56:38 +0100
> From: Will Penny <[log in to unmask]
> <mailto:[log in to unmask]>>
> To: "Emily L. Parks" <[log in to unmask] <mailto:[log in to unmask]>>
>
> Dear Emily,
>
> The function spm_vec(DCM.Ep) will transform a column vector of
> parameters into a data structure with fields .A, .B etc which correspond
> to eg. the intrinsic and modulatory connectivity matrices.
>
> Best, Will.
>
> Emily L. Parks wrote:
> > Hi All,
> >
> > In regards to DCM output, what is the order of the parameters in the
> DCM.Ep matrix? Can you point me to any references regarding the details
> of DCM output files?
> >
> > Thanks!
> > Emily Parks
> >
> >
>
> --
> William D. Penny
> Wellcome Trust Centre for Neuroimaging
> University College London
> 12 Queen Square
> London WC1N 3BG
>
> Tel: 020 7833 7475
> FAX: 020 7813 1420
> Email: [log in to unmask] <mailto:[log in to unmask]>
> URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
--
William D. Penny
Wellcome Trust Centre for Neuroimaging
University College London
12 Queen Square
London WC1N 3BG
Tel: 020 7833 7475
FAX: 020 7813 1420
Email: [log in to unmask]
URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
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